The present invention pertains to dynamically stabilized transporters and methods for maintaining such transporters under conditions of active balance while not in operation by a user.
A wide range of vehicles and methods are known for transporting human subjects. Typically, such vehicles rely upon static stability, being designed so as to be stable under all foreseen conditions of placement of their ground-contacting members. Thus, for example, the gravity vector acting on the center of gravity of an automobile passes between the points of ground contact of the automobile""s wheels, the suspension keeping all wheels on the ground at all times, and the automobile is thus stable. Another example of a statically stable vehicle is the stair-climbing vehicle described in U.S. Pat. No. 4,790,548 (Decelles et al.). A statically stable vehicle will typically remain in the position in which it is parked, subject, perhaps, to the requirement that a parking brake be set to prevent inadvertent rolling down an incline. Motion may then be resumed by mounting the vehicle and beginning locomotion from the self-same position of repose in which the vehicle was parked.
However, instead of being statically stable, a human transporter may lack inherent stability unless actively and dynamically stabilized. Such a transporter is described, for example, in U.S. Pat. No. 5,971,091 (Kamen et al., issued Oct. 26, 1999), which is incorporated herein by reference. If a rider dismounts from such a transporter and ceases to control its motion by leaning, the transporter may fall, and, depending upon the control algorithm implemented thereupon, may run away in an effort to maintain balance, or otherwise behave erratically. Such behavior is clearly undesirable.
In accordance with preferred embodiments of the present invention, a method is provided for maintaining stability of a riderless balancing transporter having two laterally disposed wheels. The balancing transporter has a region of contact with an underlying surface and is characterized by a center of mass. The method has a first step where the absence of a user aboard the balancing transporter is detected. Next, a desired transporter pitch is determined such as to establish the center of mass directly above the region of contact between the balancing transporter and the underlying surface. Then, a torque is applied to the laterally disposed wheels so as to maintain the transporter at the desired transporter pitch.
The step of applying torque to the laterally disposed wheels may include applying a torque proportional to the difference between a present transporter pitch and the target transporter pitch. It may also include applying a torque proportional to the sum of coadded terms, a first term proportional to the difference between a present transporter pitch and the target transporter pitch and a second term proportional to the pitch rate of the transporter. Two additional terms may also be coadded to obtain a motor torque command signal: one proportional to the wheel rotational velocity and a second to a time integral of the wheel rotational velocity.